The present invention relates to an electrosurgical apparatus and, more particularly, to an operation check therefor.
Electrosurgical apparatuses called "electric knives" have been in widespread use in a variety of medical and machine applications in recent years. An RF (radio frequency) current or high frequency current is supplied to an object to be cauterized or tooled and the object is seared or cut. The degree of cautery is determined by an RF current value flowing through the object, and the RF current can be controlled to a proper level by an output level setting switch or the like.
In setting an RF current value to a desired value, accurate correspondence between the value preset by the level setting switch and the actual output current value must be checked in advance. This check is particularly required in the field of medical treatment. For example, if the actual output current value is higher than the preset value, the large current endangers a patient. Therefore, before a surgical operation is performed, an operator or doctor must check in advance if output corresponding to the value preset by output setting switches is accurately produced.
A conventional electrosurgical apparatus mainly includes an RF power source, a treatment tool (an active electrode) such as a stainless wire connected to the RF power source, and an electrode plate (a passive electrode) connected to the RF power source and mounted on the patient's body. An RF current is supplied between the tip of the treatment tool and the electrode plate through the patient's body to burn or sear abnormal or injured tissue.
Japanese Patent Disclosure (Kokai) No. 58-94845 describes a conventional method of checking an RF output. According to this method, an incandescent lamp as a dummy load in place of the patient's body is connected between the tip of the treatment tool and the electrode plate. A value set by a level control switch is manually changed to visually check change in brightness level of the incandescent lamp, thus performing the preoperation check.
According to this conventional method, however, special wiring is required to connect the incandescent lamp between the electrode plate and the tip of the treatment tool, and its preparation is time-consuming and cumbersome. In addition, the brightness level of the incandescent lamp is visually checked, resulting in an inaccurate output level check. According to this conventional method, an overall system operation check including checking of a foot switch for designating an ON state of the RF current is impossible.
A clip is arranged at one end of an output check incandescent lamp cord to clamp the treatment tool, thereby providing an electrical connection therewith. However, since the tip of the treatment tool is clamped by the clip, it is often damaged by a sharp hook portion since the clip has a structure wherein a phosphor bronze plate having a width of about 2 mm is bent in a hook-like shape. If a hemostat having a rounded tip is used as the treatment tool, the clamp cannot firmly clasp the rounded tip. As a result, a proper electrical connection for the operation check cannot be achieved.
The output level can be set by changing the amplitude of the RF signal input to an amplifier for amplifying the RF output. In order to change the amplitude, a resistance ratio of an input resistance of the amplifier is changed by using a variable or fixed resistor switch.
In the conventional output level setting method, an actual output is often higher than the setting value due to variations in gain of the amplifier and poor linearity. The variations in gain of the amplifier can be controlled by a semi-fixed resistor. However, the resistance of the semi-fixed resistor varies according to vibrations, and a contact resistance varies in use over a long period of time. Even if the resistance is corrected, the preset value cannot be maintained for a long period of time. In addition, when linearity is poor, desired characteristics cannot be obtained regardless of the amplifier gain. In this case, the output setting resistance ratio must be changed. However, the resistance as a function of the rotational angle cannot be changed in a potentiometer. Alternatively, if fixed resistors are used, resistors having different resistances are changed over by using a switch.
If the output level setting value is commonly used for different output waveforms, for cutting, coagulating, and blend, a single resistance ratio is used to produce three different outputs. In this case, different variation and linearity characteristics are obtained in the different output waveforms. If three output waveforms, for cutting, coagulating, and blend, are to be selectively and independently obtained, different output level setting means can be arranged for the respective output waveforms. However, the circuit arrangement is undesirably complicated in addition to requiring cumbersome adjustment.